The present invention relates to a process for the preparation of 1,4-butanediol by hydrogenation of 1,3-butadiene diepoxide.
1,4-Butanediol is an important chemical component for syntheses and is produced worldwide; it is used, for example, as a starting material for the synthesis of epoxy resins, polyesters, polyamides and polyurethanes. Traditionally, it is prepared by hydrogenation of 2-butyne-1,4-diol, which in turn is the product of a Reppe synthesis from acetylene and formaldehyde.
The catalytic hydrogenolysis of oxiranes has been described in many publications. An overview of the hydrogenolytic cleavage of oxiranes to alcohols over various hydrogenation catalysts is given, for example, in Houben-Weyl, Methoden der Organischen Chemie, Volume VI, 1a, Part 1, 1979, pages 338 to 342. Palladium, platinum and nickel catalysts are mentioned as conventional catalysts for the oxirane cleavage with hydrogenation.
Houben-Weyl, Methoden der Organischen Chemie, Volume VI, 3, 1965, pages 442 to 446, describes the catalytic hydrogenation of asymmetric 1,2-epoxides. As a rule for the regioselectivity of the cleavage of the three-membered ring, it is stated that in general cleavage takes place between the oxygen atom and the carbon atom which carries the smallest number of hydrogen atoms.
The catalytic hydrogenation of oxiranes with cleavage of a C--O bond is also described in Houben-Weyl, Methoden der Organischen Chemie, Volume IV, 1c, 1980, pages 374 to 377. Here, it is stated that the literature data on the direction of the ring cleavage in asymmetrically substituted oxiranes are in part contradictory. Nevertheless, in contradiction to the literature reference stated in the preceding paragraph, the rule formulated is that, where there is no activation by aryl or allyl groups in asymmetrically substituted oxiranes, the C--O bond cleaved is that which is least sterically shielded, ie. whose carbon atom carries the largest number of hydrogen atoms.
The catalytic hydrogenation of 1,3-butadiene diepoxide is novel. The contradictory statements with regard to the selectivity in the ring cleavage in asymmetrically substituted oxiranes in the prior art do not permit a prediction of the product to be expected, ie. 1,4-, 2,3- or 1,3-butanediol.